Toggle a class on an element click in Angular.js

Question

In angular.js how can I toggle a css class active on and off on click of the element? I know I can use ng-class and ng-click but how do I reference itself? For example, let's say I have three buttons:

<a class="btn" ng-click="" ng-class"">First</a>
<a class="btn" ng-click="" ng-class"">Second</a>
<a class="btn" ng-click="" ng-class"">Third</a> 

Answer 1

<a ng-click="firstActive = !firstActive" ng-class"{'btn':true, 'active':firstActive}">First</a>
<a ng-click="secondActive = !firstActive" ng-class"{'btn':true, 'active':secondActive}">Second</a>
<a ng-click="thirdActive = !firstActive" ng-class"{'btn':true, 'active':thirdActive}">Third</a> 

You'll have to have separate scope variables in your controller for firstActive, secondActive, and thirdActive, all set to false by default.